Some bioceramics are of particular interest within orthopaedics and odontology, e.g. hydroxyapatite, fluoroapatite, calcium phosphates, calcium carbonate and Bioglass®. These materials can also be made more or less bio-resorbable, i.e. they may be dissolved in the body and replaced by natural tissues. This group of ceramics is explored e.g. for orthopaedic metal implants coated with a surface layer of hydroxyapatite, and various bone graft materials based on calcium phosphates and/or calcium carbonates e.g.
Precipitation of apatite in ceramic materials has also been described. A material system based on calcium aluminate and a hydration liquid containing water solvable phosphates to enhance apatite formation are described in: “System for dental filling materials or implant material, and powder material and hydration liquid” (SE 0201920-6), and “Bonding system for dental filling material or implant material, and powder material and hydration liquid and method to create bonding” (SE 0201921-4). These patent applications do not include material compositions for coatings or techniques to achieve coatings.
A range of established surface coating techniques have been described. The most established techniques for deposition of ceramic coatings are Chemical Vapour Deposition, Physical Vapour Deposition, Thermal Spraying, Plasma Spraying and Electrolytic Deposition. Surface coatings may also be produced with powder technology.
A great disadvantage with these techniques for deposition of ceramic coatings, with the exception of electrolytic deposition, is the elevated temperatures involved in their processing. This sets limitations to the selection of substrate materials, and to the chemical structures and phases that can be achieved. To the disadvantage also counts the complexity of the required equipments, such as the gas-tight vacuum arrangements needed for chemical and physical vapour deposition, and the high-temperature and presses required in powder technology.
A recently developed method for the deposition of coatings based on chemically bonded ceramics is described in the patent applications SE-0104440-3, “Coating method and coated devices” (filed December 2001); and SE-0200637-7, “Ceramic surface layers and coated devices (filed March 2002). These patent applications describe a coating deposition method comprising the steps: pre-treatment of substrate; preparation of curable slurry with hydraulic components, deposition of the slurry as a coating on a substrate and hardening of the coating through hydration. Alternatively, layers of non-hydrated hydraulic powders are deposited on the substrate, and hydrated in an additional step.
U.S. Pat. No. 5,480,438-A, filed Sep. 22, 1993, describes ceramic multi-layers comprising a metallic implant base coated with two bioactive layers. The inner layer can be comprised of calcium aluminate and the outer layer of apatite and/or calcium phosphate. This multi-layer is manufactured by other methods, mainly plasma spraying, than the methods used in the present application. Nor does U.S. Pat. No. 5,480,438-A disclose multi-layers comprised of hydrated ceramic.